There are two kinds of technologies available in the field of power converting process. One of which is analog technology, namely common-used analog power amplification, which converts DC power into the power in a signal form in the linear working area where a device operates. Because the efficiency of energy conversion is extremely low, for example for a power amplifier for class A, the efficiency of which is usually less than 30%, namely η<30%. Most of energy is consumed and converted into heat energy, in order to improve efficiency and reduce heating, improvement has been made to analog power amplifier. Thus, a kind of power amplifier for class B is developed, theoretically its limit efficiency is 78%. Actually, it can only achieve about 50% at most. Well, the value of THD+N (Total Harmonic Distortion plus Noise) is more than 5%, and the distortion has not been accepted. Therefore, power amplifier for class AB1 and power amplifier for class AB2 were developed as compromise between class A and class B. In fact, power amplifier for class AB1 and class AB2 arc results film re-adjusting and redistributing power and distortion status of the power amplifier for class A and the power amplifier for class B. Usually, power amplifier that are made by using this kind of technology can achieve about 30% in efficiency (namely η≈30%), and 0.5% in THD. Now, this kind of technology is applied to most of power amplifiers.
The other one is digital technology. A common-used digital power amplifier is made by using this kind of technology. The specifics are as follows: all of its components are working under on-and-off status. So, their status can be expected It can achieve high efficiency. As to this point, digital technology is much better than analog technology. By adopting pulse width modulation technology, the digital power amplifier converts source power into series of pulse power under the control of signal. The product of duty of each pulse and pulse amplitude equals to the value of signal amplitude during the corresponding period (please see FIG. 1). Therefore, the spectrum of said series of pulse contains signal spectrum, and the power in signal form can be obtained with filtering. In theory, if the sample frequency is higher than the highest frequency component by two times, signal can be restored completely and signal power can be output under brand limit. Actually, due to the influence of such factors as various components' characteristic, driving, power source, temperature etc., pulse may subject to distort unpredictably. Thus, the distortion of this kind of power amplifier is too serious in practical application, and the approximate value of its THD can even reach up to 10% when outputting bigger signal.
In addition, theoretically, the power amplifier using pulse width modulation can be accurately realized and would not produce the result of distortion. However, because the on-and-off duration of apparatuses and circuit parameters lead inclination of front and back edge of pulse, and the voltage drops across the inner resistance of power source and switch components cause the inclination of the top of output pulse, as shown in FIG. 2, the actual pulse area (S0′) doesn't equal to the ideal PWM area (S0). This difference can be produced in each pulse. Eventually, wave distortion occurs. The higher the frequency is and the bigger the power is, therefore the more serious the distortion will be.
Now, in the field of electronic technology, the current status of power processing is that the efficiency of an analog power amplifier is too low, and the distortion of a digital power amplifier with pulse modulation is unacceptable.